1. Field of the Invention
The present invention relates to an automatic anti-skid brake control system for a motor vehicle. More particularly, the present invention relates to an anti-skid brake control system which includes wheel sensors for determining the speed of each individual vehicle wheel, an evaluation circuit to which the wheel speed sensor signals are applied and which generates brake pressure control signals as a function of the wheel speeds, and brake pressure control valves, responsive to the brake pressure control signals, for varying the brake pressure at the vehicle wheels. In the evaluation circuit, the wheel speed signals are used to obtain at least one reference speed value that approximates the vehicle speed characteristics so as to determine the slippage of any wheel. Such slippage, together with the wheel speed signals and the vehicle deceleration, is used to control the brake pressure.
2. Prior Art
The German patent publication No. 2,313,763 to which U.S. Pat. No. 3,907,378 corresponds discloses an automatic anti-skid brake control system of the aforementioned type. This automatic anti-skid brake control system, which also generates slippage signals and therefore requires a reference speed, is provided with a vehicle deceleration sensor which is used to determine, in short repeated intervals, whether the braking effect of the vehicle is more efficient with or without the anti-skid control. In this case, the vehicle deceleration sensor consequently serves to monitor the anti-skid control.
It is also known from the German patent publication No. 2,558,712, to which U.S. Pat. No. 4,053,188 corresponds to formulate the reference speed which is required for slippage control by referring to the speed signals of two or more wheels included in the control system and to select for reference speed formulation the most rapidly turning wheel. The wheel speed signals V.sub.R trigger the possibly necessary slope of the reference speed signals either without modification or with at least one prescribed slope. To decrease the reference speed V.sub.Ref in case of instability (V.sub.R &lt;V.sub.Ref), there are several slopes which can be activated as a function of the determined rotational behavior of the wheel slope according to a prescribed algorithm.